In order to achieve improved efficiency, a high turbine inlet temperature is used in standard gas turbines. As a result, there can arise relatively high NOx emission levels and relatively high life cycle costs. These can be mitigated with a sequential combustion cycle, wherein the compressor can deliver a relatively higher pressure ratio one. The main flow passes the first combustion chamber (for example, using a burner of the general type as disclosed in EP 1 257 809 or as in U.S. Pat. No. 4,932,861, also called an EV combustor, where the EV stands for environmental), wherein a part of the fuel is combusted. After expanding at the high-pressure turbine stage, the remaining fuel is added and combusted (for example, using a burner of the type as disclosed in U.S. Pat. No. 5,431,018 or U.S. Pat. No. 5,626,017 or in U.S. Patent Application Publication No. 2002/0187448, also called SEV combustor, where the S stands for sequential). Both combustors contain premixing burners, as relatively low NOx emissions can require high mixing quality of the fuel and the oxidizer.
Because the second combustor is fed by expanded exhaust gas of the first combustor, the operating conditions can allow self ignition (spontaneous ignition) of the fuel air mixture without additional energy being supplied to the mixture. To prevent ignition of the fuel air mixture in the mixing region, the residence time therein should not exceed the auto ignition delay time. This can ensure flame-free zones inside the burner but poses challenges in obtaining appropriate distribution of the fuel across the burner exit area.
SEV-burners can be designed for operation on natural gas and oil only. Therefore, the momentum flux of the fuel can be adjusted relative to the momentum flux of the main flow so as to penetrate into the vortices. The subsequent mixing of the fuel and the oxidizer at the exit of the mixing zone can be just sufficient to allow relatively low NOx emissions (mixing quality) and avoid flashback (residence time), which can be caused by auto ignition of the fuel air mixture in the mixing zone. The cross flow injection used in the known SEV-fuel injection devices (SEV fuel lances) can necessitate high-pressure carrier air supply, which can reduce the overall efficiency of the power plant.